Split boots and method of connecting the boots, depositing agent, and heating body

ABSTRACT

A protruding part formed on one split end part of a boot is temporarily fixed to a recessed part formed on the other split end part in the state where step-shaped hook portions formed on one-end thereof are engagingly locked to each other, and connected by welding, fusion or adhesion. The protruding part is hooked only in one thickness directional side. An overlapping protruding part formed on the non-hook side (inner side) of the recessed part is connected extending over the inside surface of the protruding part and the inside surface of the split end part continued thereto.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a boot used for sealing, for example, theoperating part of a universal joint, and a connecting method, weldingagent and heating body therefor.

2. Description of the Prior Art

In this type of boots, mounting parts present on both axial ends thereofare mounted, for example, on the outer race and joint shaft of auniversal joint, whereby the bellows-formed flexible part of the boot isflexibly expanded and contracted to prevent the intrusion of an externalforeign matter to the operating part of the universal joint and,further, to seal the oil and fat such as grease filled in the operatingpart.

In a conventional split type boot, which is one type of theabove-described boots, a rubber-made boot is divided in onecircumferential part. A plurality of fasteners consisting of maleconnecting member and female connecting member arranged at prescribedintervals is integrally provided on each of the circumferentiallyopposed split end parts. In mounting, the boot is put over a universaljoint from the side by opening the split part. The fasteners are coupledand also adhered together by an adhesive, whereby the split end partsare mutually connected in the closely fitted state.

The boot is rotated in the state where the shaft centers of the outerrace and joint shaft having both the axial end mounting parts fixedthereto are mutually inclined. Accordingly, the bellows part repeatsbending and stretching motions every half period of the rotation. In thesplit boot, the repeated bending and stretching of the mutually adhereddivided end parts induce the danger of the hardened adhesive layercausing a deterioration such as crack by fatigue, resulting in the earlyleakage of the grease within the universal joint. Further, it isnecessary to provide the male connecting member and female connectingmember of the fasteners in the divided end parts with high precision. Itis also necessary to ensure the sealing property of the fasteners byapplying a coating agent or the like because of its low sealingproperty. Further, their scanty following property to the bending andstretching deformation of the boot induces the danger of its breakagewithin a short period.

SUMMARY OF THE INVENTION

This invention has an object to improve the sealing performance andfatigue strength in the opposed split end parts of a split type boot andalso improve the working property in mounting.

A split type boot according to one embodiment of this invention is acylindrical boot divided in one circumferential part, in which aprotruding part and recessed part extending along the sectional form ofthe boot are formed on the circumferentially opposed split end parts tobe integrally connected in mounting, respectively. The protruding parton one split end part and the recessed part on the other split end parthave the forms to be hooked (engagingly locked) to each other in onethickness directional side. An overlapping protruding part is protrudedlonger than the protruding part on the non-hook (lock) side in therecessed part, and connected extending over the protruding part and theone split end part.

Both the axial end mounting parts of the boot are preferably formed of arubber-like elastic material more elastic than the boot. The boot ismounted on the outside surface of a counter material through a packingdivided in one circumferential part.

A split type boot according to another embodiment of this invention isprovided with an open part formed by dividing one circumferential partthereof, and mounted by connecting the open part after covering amounting member such as universal joint. The open part is connected byheating and welding it by a heating body having self-heating property.

In a connecting method for a split boot according to a furtherembodiment of this invention, the boot has an open part formed bydividing one circumferential part thereof, and the open part isconnected after covering a mounting member such as universal joint. Aheating body having self-heating property is brought into contact withor approached to the open part to heat and weld the open part by theheating body.

A welding agent according to an additional embodiment of this inventionis a welding agent used in the connection of the open part formed bydividing one circumferential part after covering a mounting member suchas universal joint, and it is applied to the opposed surfaces of theopen part to weld the opposed surfaces together.

A preferable welding agent according to this invention consists of asolvent for dissolving a thermoplastic elastomer. The welding agent isformed of a simple body or mixture of solvents, for example,dimethylformamide, tetrahydrofuran, toluene, ethyl acetate, methyl ethylketone, acetone, cyclohexanone, and dichloromethane.

A heating body according to another embodiment of this invention is aheating body used in the connection of the open part formed by dividingone circumferential part, which has self-heating property, and is fixedto the boot to heat and weld the open part in contact with or adjacentto the open part.

A preferred heating body according to this invention is formed of anamorphous bag and a heating component put therein so as to be deformablefollowing the bellows form of the boot.

Further preferably, an irregular form laid along the irregularities ofthe bellows is preliminarily imparted to the outer surface of theheating body so as to closely fit to the open part along the bellowsform of the boot.

According to a preferred split type boot of this invention, satisfactorysealing property is ensured for the mutually connected split parts ofthe boot in the state mounted on a mounting member such as universaljoint, because the protruding part and recessed part are continuouslyextended on the split end parts of the boot, and the fitting surfacesthereof are integrated together by welding, fusion or adhesion. Further,because a large connecting area can be ensured by forming, on thenon-hook side of the recessed groove, the overlapping protruding part tobe connected extending over the protruding part and the one split endpart continued thereto.

Further, the protruding part is set to the form to be hooked (engaginglylocked) with the recessed part in one thickness directional side,whereby the split end parts can be thinned, compared with the case offorming the hook part (locking part) on both thickness directionalsides. Therefore, the insert resistance in the temporary connection ofthe split end parts can be minimized by insert-engaging the protrudingpart with the recessed part, and the superposing protruding portion alsoguides the insertion, so that the temporary connecting work can beeasily performed. Further, since the increase in stress by the repeatedbending and stretching deformation can be suppressed, the fatiguedurability can be improved.

When both the axial end mounting parts of the boot are mounted on theoutside surface of a counter member such as universal joint throughpackings formed of a rubber-like elastic material more elastic than theboot, the sealing property in the mounting parts can be improved.

In a preferable boot according to this invention, the boot ismanufactured without mounting fasteners on the opposed surfaces of theopen part, and when the boot is mounted on the circumference of amounting member such as universal joint, a welding agent is applied tothe opposed surfaces of the open part to mutually weld the opposedsurfaces together. In such a welding of the open part, the open part isheated and welded by a heating body having self-heating property,whereby the welding reaction or connecting reaction is promoted. Theopen part connected by welding is excellent in sealing property sincethe opposed surfaces are integrated together. Further, it is deformablefollowing the deformation of the bellows part. To have self-heatingproperty means exhibiting the heating effect for itself in use andrequiring no supply of external energy as electric power. To ensure theconnecting property by welding, a thermoplastic elastomer is preferablyused as the material of the split type boot. To sufficiently exhibit theperformance as the boot, a polyurethane thermoplastic elastomer orpolyester thermoplastic elastomer highly strong and excellent indurability are preferably used.

In a preferred connecting method for a boot according to this invention,the boot is manufactured without mounting fasteners on the opposedsurfaces of the open part, and when this boot is mounted on thecircumference of a mounting member such as universal joint, a weldingagent is applied to the opposed surfaces of the open part to weld theopposed surfaces together. In such a welding of the open part, theheating body having self-heating property is brought into contact orapproached, and the open part is heated and welded by this heating body,whereby the welding reaction or connecting reaction is promoted. Theopen part connected by welding is excellent in sealing property sincethe opposed surfaces are integrated together. Further, it is deformablefollowing the deformation of the bellows part. As the heating bodyhaving self-heating performance, a one mainly composed of iron powder,water, activated charcoal and salt or of a metal oxide and water, andgenerating heat mainly by oxidization reaction or reduction reaction ispreferably used. Further, any other materials having self-heatingperformance can be used.

The heating body used for the connection of the open part is preferablyformed of a permeable bag of paper, nonwoven fabric or cloth and aheating component mainly composed of iron powder, water, activatedcharcoal and salt or of a metal oxide and water and put therein. When ashielding film-like outer packaging enclosing this heating body isopened, the moisture in the air touches the iron to cause the oxidationreaction of the iron, or the metal oxide is reacted with water to causethe reduction reaction. High heat is generated according to this, sothat the open part can be heated and welded by this high heat. In orderto satisfactorily transfer the heat of the heating body to the open partin spite of the presence of the irregularities (mountain/valley) by thebellows part on the outer surface of the boot, the heating body ispreferably closely fitted to the overall outer surface of the open partby putting the heating component in an amorphous bag or preliminarilyimparting the irregular form laid along the irregularities of thebellows to the outer surface of the heating body. According to this, theheating body is closely fitted or approached to not only the protrudingpart (mountain part) of the bellows but also the recessed part (valleypart) thereof to raise the temperature of the recessed partsubstantially equally to the temperature of the protruding part. Thus,the temperature of the whole open part can be uniformly raised, and thewelding time can be thus consequently shortened.

To heat the open part, a dryer for blowing hot air, for example, can beused. In this case, however, a person must perform the work with thedryer in its hand in constant attendance until the welded part issufficiently dried. A constraining means must be separately provided sothat the open part is not opened in the middle of welding to keep theopen part in the closed state. Further, the blowing of hot air maypossibly cause a large dispersion of temperature between the partexposed to the hot air and the part not exposed to the hot air.

Contrary to this, when the heating body is fixed to the outer surface ofthe open part of the boot to perform the welding, the work can beprogressed without attendance of a person in drying. The open part canbe kept in the closed state until the welded part is dried withoutseparately providing the different constraining means. Further, theheating temperature can be easily made constant. An external heat energysource such as power source apparatus or heating light is dispensedwith.

To fix the heating body to the outer surface of the open part of theboot, a mounting means such as adhesive sheet, adhesive tape, tyingcord, stretchable cloth or hook-and-loop fastener is preferably used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a split type boot according to onepreferred embodiment of this invention.

FIG. 2 is a sectional view taken along line II-II′ in FIG. 1.

FIGS. 3A and 3B are enlarged sectional views of essential parts of thesame split type boot, wherein FIG. 3A shows the non-connected state, andFIG. 3B shows the connection completed state.

FIG. 4 is a sectional view showing a comparative example of theprotruding part and recessed part formed on the split end parts (openpart) of the split type boot.

FIG. 5 is a perspective view of a split type boot according to anotherembodiment of this invention.

FIG. 6 is a perspective view showing one example of a heating body formanufacturing the split type boot according to this invention.

FIG. 7 is a sectional view of the split type boot in the state where theheating body is fixed thereto.

FIG. 8 is a perspective view of the split type boot in the state wherethe heating body is fixed thereto.

FIG. 9A is a perspective view showing another example of the heatingbody, and FIG. 9B is a perspective view of the heating body in thefolded state.

FIG. 10 is a perspective view showing another example of the heatingbody.

FIG. 11 is a perspective view showing a further example of the heatingbody.

FIG. 12 is a perspective view showing an additional example of theheating body.

FIG. 13 is a sectional view of a split type boot according to a furtherembodiment of this invention.

FIG. 14 is a sectional view showing the mounted state of the boot ofFIG. 13.

FIGS. 15A and 15B are perspective views showing the connecting structureand sealing structure of the major diameter-side end part of the boot.

FIGS. 16A and 16B are perspective views showing another connectingstructure and sealing structure of the major diameter-side end part ofthe boot.

FIG. 17 is a sectional view of a split type boot according to anotherembodiment of this invention.

FIGS. 18A, 18B, and 18C are sectional views taken along lines A—A, B—B,and C—C in FIG. 17, respectively.

DETAILED DESCRIPTION OF THE INVENTION Embodiment of FIGS. 1-3

FIGS. 1-3 show a split type boot according to one preferred embodimentof this invention.

The outline of the split type boot is described. A protruding part 16formed on one split end 14 of a boot 1 is temporarily connected to arecessed part 17 formed on the other split end 15 in the state wherestep-shaped hook portions 162 a, 172 a formed on one-end sides thereofare engagingly locked to each other, and then connected by welding,fusion or adhesion. The protruding part 16 is hooked only in onethickness directional end of the boot. An overlapping protruding part173 formed on the non-hook side (inside) of the recessed part 17 isconnected extending over the inside surface 16 a of the protruding part16 and the inside surface of the split end 14 continued thereto.

In FIG. 1, the whole body of the boot 1 is molded of a thermoplasticelastomer. The thermoplastic elastomer, which is abbreviated as TPE aswell known, has the properties as elastomer (rubber elastic body) atordinary temperature and shows plastic flowing property at hightemperature, or the thermoplastic elastomer has a molecular structure ormicro-dispersed structure in which a rubber component having entropyelasticity is coupled with a constraining component for preventing theplastic deformation at ordinary temperature. Examples of the TPE includepolyurethane thermoplastic elastomer (TPU) and polyester thermoplasticelastomer (TPEE) excellent in ozone resistance, strength, coldresistance, grease resistance and fatigue resistance.

In the embodiment of FIGS. 1-3, the polyurethane thermoplastic elastomerexcellent in strength, ozone resistance and fatigue resistance, comparedwith general rubber material, is preferably adapted as the material ofthe boot 1. Particularly, a polyether type polyurethane thermoplasticelastomer obtained by reacting a polyoxymethylene glycol having a numberaverage molecular weight of 1500-2500 with a chain extender and anorganic diisocyanate is preferred. A one having a melting viscosity at200° C. of 0.5×10⁴-1.0×10⁶ poise is more preferable because of excellentwaterproof property and moldability. In this case, for example, the NCOindex (NCO equivalent number/OH equivalent number) of theabove-mentioned polyoxymethylene glycol, chain extender and organicdilsocyanate is 1.0-1.1. The chain extender consists of, for example, alow molecular weight diol having 2-10 carbon atoms, and the organicdiisocyanate consists of, for example, 4,4′-diphenylmethanediisocyanate.

The boot 1 has a minor diameter mounting part 11 formed on one axial end(lateral direction of FIG. 1), a major diameter mounting part 12 formedon the other axial end, and a thin bellows part 13 formed between boththe mounting parts 11, 12. The bellows part 13 is formed of repeatedlyformed mountain parts 13 a and valley parts 13 b. Circumferentiallyextending band mounting grooves 11 a, 12 a are formed on the outsidesurfaces of the mounting parts 11, 12, respectively, so that bands forfastening the mounting parts 11, 12 onto the outside surfaces of thejoint shaft and outer race of a universal joint, for example, can bewound on the band mounting grooves 11 a, 12 a, respectively.

As shown in FIG. 2, which is a sectional view taken along II-II′ in FIG.1, the boot 1 is cut or divided in one circumferential part, and hassplit edges or split end parts 14, 15 mutually opposed in both thecircumferential sides. The split end parts 14, 15 may be called alsoopen end parts since opened before connection. In these end parts 14,15, the parts extending along the bellows part 13 are increased inthickness toward the inner side so as to be properly thicker than thebellows part 13.

A protruding part 16 is projectingly formed on one split end part 14 ofthe boot 1 in the direction opposite to the other split end part 15. Agroove-like recessed part 17 corresponding to the protruding part 16 isformed on the other split end part 15. The protruding part 16 and therecessed part 17 are extended over the whole axial length of the bellowspart 13 along the sectional form of the boot 1.

The protruding part 16 is formed of, as shown in FIG. 3, a neck part 161protruded from a position closer to the inner side of the end surface 14a of the one split end part 14 in the boot 1 and a head part 162 formedat the tip of the neck part 161. The head part 162 has a step-shapedhook portion 162 a standing up outward from the outer surface 161 a ofthe neck part 161 and an outside tapered surface 162 b reduced indiameter from the periphery of the step-shaped hook portion 162 a towarda tip 162 c. The inside surface 16 a of the protruding part 16constitutes a flat surface continued to the inside surface 14 b of theone split end part 14.

The recessed part 17 has a sectional form corresponding to theprotruding part 16. Namely, the recessed part 17 is formed of a neckpart receiving part 171 extended from the end surface 15 a turned to theone split end part 14 side in the other split end part 15 and a headpart receiving part 172 extensively formed in the deep part thereof. Thehead part receiving part 172 has a step-shaped hook portion 172 astanding up outward from the outer surface 171 a of the neck receivingpart 171 and an outside tapered surface 172 b reduced in diameter fromthe periphery of the step-shaped hook portion 172 a toward the innerpart of the split end part 14. The inner side of the recessed part 17forms an overlapping protruding part 173 extending longer than theprotruding length of the protruding part 16 toward the one split endpart 14. Its outside surface 173 a is formed in conformation to theinside surface 16 a of the protruding part 16 and the inside surface 14b of the one split end part 14 continued thereto.

In FIGS. 3A and 3B, the lower side corresponds to the inner side of theboot.

FIG. 4 shows a comparative example where step-shaped hook portions a, bare formed on both the outside and inside surfaces of a protruding part16′ and a recessed part 17′, respectively. Compared with thiscomparative example, the thickness t of the split end parts 14, 15 canbe minimized in the embodiment of FIG. 3 (the protruding part 16 has thestep-shaped hook portion 162 a formed only on one thickness directionalside (outer side) thereof, and the recessed part 17 has also the formcorresponding thereto).

As shown in FIG. 1, grommets 2, 3 are arranged on the inside of both theaxial end mounting parts 11, 12 of the boot 1 as packing, respectively.The grommets 2, 3 are molded of a rubber material, for example, NBR(nitrile rubber), which is more elastic than the thermoplastic elastomerforming the boot 1 and excellent in characteristics such as oilresistance, cold resistance and compression permanent distortion, andeach of the grommets 2, 3 is divided in at least one circumferentialpart similarly to the boot 1.

The grommet 2 arranged on the inside of the mounting part 11 of the boot1 has a strip fitting groove 11 capable of fitting with the inside partof the mounting part 11 on the outside surface and a circumferentiallycontinued seal protruding part 22 formed on the inside surface. In thesame manner, the grommet 3 arranged on the inside of the mounting part12 of the boot 1 has a fitting stepped part 31 capable of fitting withthe inside part of the mounting part 12 on the circumferential surfaceand a circumferentially continued seal protruding part 32 formed on theinside surface.

The above-mentioned split type boot of FIGS. 1-3 is mounted as thesealing means of, for example, a universal joint not shown, by arrangingthe universal joint in the inside thereof. At the time of mounting, thesplit end parts 14, 15 are opened and put over the universal joint fromthe side so that the minor diameter-side mounting part 11 and the majordiameter-side mounting part 12 are situated on the joint shaft side ofthe universal joint and on the outer race side, respectively.Thereafter, the protruding part 16 of the one split end part 14 isinserted and fitted, as shown in FIG. 3B, to the recessed part 17 of theother split end part 15 from the separated state shown in FIG. 3A,whereby the split end parts 14, 15 are temporarily connected together.

In the above temporarily connecting process, the protruding part 16 isguided by the overlapping recessed part 173 protruded long from theinside of the recessed part 17 toward the split end part 14 side. Whenthe head part 162 of the protruding part 16 is inserted to the neck partreceiving part 171 of the recessed part 17, the recessed groove 17 isdeformed so as to be open once by the interference with the outsidetapered surface 162 b of the head part 162. Thereafter, the head part162 is perfectly inserted into the head receiving part 172 of therecessed part 17, whereby the protruding part 16 and the recessed part17 are laid in the substantially closely fitted state as shown in FIG.3B. The boot 1 consisting of thermoplastic elastomer is molded so thatthe split end parts 14, 15 are in opened state to some degree, as shownin FIG. 2, when no external force is added thereto. Therefore, althoughthe both are apt to open by the elastic property possessed by thethermoplastic elastomer, the temporarily connected state can be keptsince the step-shaped hook portions 162 a and 172 a are mutually hookedin the state shown in FIG. 3B.

The grommet 2 is arranged on the joint shaft outside surface of theuniversal joint so as to embrace it from the side. The minordiameter-side mounting part 11 of the boot 1 is arranged so that theinside part is fitted to the strip fitting groove 21 formed on theoutside surface of the grommet 2, and fastened by a metal band wound onthe band mounting groove 11 a. The grommet 3 is similarly arranged onthe outer race outside surface of the universal joint so as to embraceit from the side. The major diameter-side mounting part 12 of the boot 1is arranged so that its inside part is fitted to the fitting steppedpart 31 formed on the outside surface of the grommet 3, and fastened byanother metal band wound on the band mounting groove 12 a.

The mounting parts 11, 12 of the boot 1 consisting of thermoplasticelastomer are fixed to the joint shaft circumferential surface and outerrace circumferential surface of the universal joint through the grommets2, 3 consisting of nitrile rubber fitting well with the counter materialand rich in elasticity. Particularly, the mounting parts 11, 12 areclosely fitted to the grommets 2, 3 in the tongue-and-groove fittingstate by the fastening force of the metallic bands from the outside. Theseal surface pressure to the joint shaft outer outside surface and outerrace outside surface is locally increased in the seal protruding parts11 b, 12 b of the grommets 2, 3. Consequently, a satisfactory sealedstate can be provided.

The split end parts 14, 15 temporarily connected by insert-engaging theprotruding part 16 with the recessed part 17 is welded by use of, forexample, a welding agent. The split end parts 14, 15 are connected toeach other by such a method. In this case, the welding agent ispreliminarily dropped and spread over the mutual connecting surfaces ofthe split end parts 14, 15 and the connecting surfaces among theprotruding part 16, the recessed part 17 and the overlapping protrudingpart 173. The thermoplastic elastomer on the surface layer part of theconnecting surfaces is temporarily fused, and the welding agent is thenevaporated, whereby a continued thermoplastic elastomer tissue is formedto form the integrally connected state.

When the boot 1 is formed of a polyether type polyurethane thermoplasticelastomer, the welding agent used for the connection of the split endparts 14, 15 is suitably prepared by dissolving the polyurethanethermoplastic elastomer to a solvent consisting of a mixture ofdimethylformamide and tetrahydrofuran (THF) to regulate the viscosity(mPa·s) to 100-10000. By such a regulation of the viscosity, the solventis hardly sagged in the application, and the working property can beimproved. As the solvent, ethyl acetate, acetone, methyl ethyl ketone(MEK), cyclohexanone, or a mixed solvent obtained by adding a smallquantity of chloroform, N-methyl-2-pyrolidone or dibutyl ether to thedimethylformamide can be used.

To mutually connect the split end parts 14, 15 temporarily connected bythe protruding part 16 and the recessed part 17, means such as fusion byheating or adhesion by dope cement can be adapted in addition to theabove welding by the welding agent. In the connection by fusion, it ispreferred to temporarily heat the fitting parts of the split end parts14, 15 or adding a high frequency vibration thereto. Namely, theconnection is performed by temporarily heating and fusing thethermoplastic elastomer in the fitting surfaces of the split end partprotruding part 16 and recessed part 17 to form a continuedthermoplastic elastomer tissue.

The split end parts 14, 15 of the boot 1 are integrally connected toeach other by the above work. A wide connecting area can be ensured bythe overlapping protruding part 173. The leakage of the grease withinthe universal joint through the connecting part of the split end parts14, 15 or the intrusion of external mud water or dust through theconnecting part of the split end parts 14, 15 can be effectivelyprevented. Although the split end parts 14, 15 are formed thick,compared with the bellows part 13, they can be thinned, compared withthe one having a mushroom-shaped sectional hook structure shown in FIG.4. Therefore, the bending and stretching deformability can be ensured inthe split end parts 14, 15. The fatigue resistance in the split endparts 14, 15 can be also improved to prevent the early peeling of theconnecting surfaces.

The boot 1 is molded of the thermoplastic elastomer excellent instrength, ozone resistance and fatigue resistance, compared with generalrubber material and having waterproofing property. Therefore, the boot 1hardly causes the leakage of grease by fatigue breakage in the boot 1connecting part and exhibits excellent durability.

In the above embodiment, for example, the grommets 2, 3 as packing canbe preliminarily integrated to the insides of the mounting parts 11, 12of the boot 1 by means of fitting, or integrated to the boot 1 byadhesion.

The product endurance test and material waterproof test were performedwith respect to the embodiment of FIGS. 1-3.

EXAMPLE

An organic diisocyanate corresponding to a theoretical quantity wasprepared by mixing 660 parts of polyoxymethylene glycol having a numberaverage molecular weight of 1700 with 55 parts of 1,4-butane diol aschain extender, 252.5 parts of 4,4′-diphenylmethane diisocyanate wasadded thereto, and the resulting mixture was reacted at 160° C. for 10minutes. The resulting polyether type polyurethane thermoplasticelastomer was used to injection mold a split type boot of the form shownin FIGS. 1 and 2. The connection of the split end parts 14, 15 of theboot 1 was performed by welding by use of a welding agent. The weldingagent used was prepared by dissolving a polyether type polyurethanethermoplastic elastomer of the same material as the member to beconnected to a solvent consisting of dimethylformamide to regulate theviscosity (mPa·s) to 1000. After applying the welding agent, the boot 1was stably held at room temperature for 15 minutes.

COMPARATIVE EXAMPLE

By use of a polyolefine thermoplastic elastomer (Santoprene 101-87:manufactured by AES), the split type boot of the form shown in FIGS. 1and 2 was injection molded. The connection of the split end parts 14, 15of the boot 1 was performed by welding by use of a welding agent. As thewelding agent, dimethylformamide was used, and after applying thewelding agent, the boot was stably held at room temperature for 15minutes.

The evaluation (product endurance test) was performed as follows.

Each of the thus-manufactured boots of the example of this invention andits comparative example was mounted on an oscillating rotary testingdevice to measure the endurance. The endurance was judged according tothe time when the grease is leaked from the boot after starting theoperation.

Test Condition

Temperature: Room temperature Oscillating angle: 25-40° Oscillatingcycle: 30 times/min Rotational Frequency: 600 rpm

The test result was as follows.

In the product endurance test, the grease leakage was confirmed at 20minutes after starting the test in the comparative example. Contrary tothis, it took 280 minutes for the occurrence of grease leakage in theexample of this invention, from which it was thus confirmed that thesplit type boot molded of the polyether type polyurethane thermoplasticelastomer was more excellent in durability.

When a polyester type polyurethane thermoplastic elastomer was adaptedas the material of the boot 1, also, the same effect described above canbe provided. Although the form of hooking the protruding part 16 withthe recessed part 17 on the outer side is adapted in the embodiment ofFIGS. 1-3, the form of hooking the protruding part 16 with the recessedgroove 17 on the inner side and providing the overlapping protrudingpart 173 on the outer side of the recessed groove 17 can be alsoadapted.

Embodiment of FIGS. 5-12

A split type boot 1 according to the embodiment of FIG. 5 is cylindricalas the whole, and provided with an annular minor diameter-side mountingpart (also referred to as fixing part) 11 on one end open part. The boot1 has an annular major diameter-side mounting part 12 having a diameterlarger than the minor diameter-side mounting part 11 on the other endopen part. Further, a bellows part 13 is integrally molded between boththe mounting parts 11, 12. The whole boot 1 is molded of a thermoplasticelastomer. The thermoplastic elastomer is a polyurethane thermoplasticelastomer.

The boot 1 has an open part (also referred to as split member,connecting part or cut part) 18 formed by dividing and opening onecircumferential part over the whole length. The open part 18 isconnected by heating and welding it by a heating body havingself-heating property (referred also to as heating agent, heatingelement, or heat generating agent).

The boot 1 is manufactured without forming fastener parts on the opposedsurfaces 18 a, 18 b of the open part 18, and mounted on thecircumference of a universal joint by opening the open part 18 to putthe boot 1 over the universal joint through the open part 18, andconnecting the open part 18. At this time, the minor diameter-sidemounting part 11 is fixed to the drive shaft side by a band, and themajor diameter-side mounting part 12 is similarly fixed to the universaljoint side by another band.

Heating Body

A heating body 41 comprises a permeable bag 42 consisting of paper,nonwoven fabric or cloth and a heating component (not shown) mainlycomposed of iron powder, water, activated charcoal and salt, or of ametal oxide and water put in the bag 42. When an outer packaging (notshown) consisting of a shielding film is opened in use, the moisture inthe air touches the iron component to cause the oxidation reaction ofthis iron component, or the metal oxide and water cause a reductionreaction. According to this, high heat is generated. The open part 18can be heated and welded by this high heat. The bag 42 containing theheating component has freely deformable amorphous property. One surfaceof the bag 42 forms an adhesive surface 43 by sticking an adhesive sheetso that the heating element 41 can be fixed to the outer surface of theopen part 18 of the boot 1. A heating surface 44 for generating highheat is set on the same plane.

Although a chemical reaction type heating material is used for the aboveheating, a phase change type heat reserving material generating heat inthe crystallization of a crystalline material from the supercooled statecan be also used. Examples of the heat reserving material include sodiumacetate hydrate and the like. Since this material is liquefied incontrast to the former powdery material, it is further fitted well tothe form of the boot.

As shown in FIGS. 7 and 8, the heating body 41 is stuck extending overthe outer surface of the open part 18 of the boot 1. This adhesive forceretains the open part 18 in the closed state so as not to be open duringthe welding work. The bag 42 is properly deformed along theirregularities (mountain/valley) of the outer surface of the bellowspart 4 of the boot 1 and closely fitted to the irregularities in a widearea. Therefore, the heat generated in the heating body 41 isefficiently transferred to the open part 18. The open part 18 can beefficiently heated and welded by this efficiently transferred high heat.

As shown in FIGS. 9A and 10, an irregular form 45 is preliminarilyformed on the outer surface of the heating body 41, and arrangedaccording to the irregularities of the outer surface of the bellows part4. According to such a method, also, the heating surface 44 of theheating element 41 can be brought into contact with the boot 1 in a widearea. The heating body 41 of FIG. 9A has a plurality of irregularities.The heating element 41 of FIG. 10 has one protruding part.

In the storage of the heating body 41, the outer surface is folded in anirregular form as shown in FIG. 9B. Therefore, the outer surface ispreferably covered with a packaging consisting of a stretchablematerial, for example, nylon tights, nylon stockings or the like so thatthe moisture in the air can be shielded.

As the mounting means for fixing the heating body 41 to the outersurface of the boot 1, various fixing means are adaptable in addition tothe above adhesive sheet.

FIGS. 11 and 12 show examples of the fixing means. In the example ofFIG. 11, a plurality of tying cords 46 are mounted on both sides of theheating body 41 as a commercially available body warmer. The tying cords46 are laid around the boot 1, and the tips thereof are tied together.

In the example of FIG. 12, a pair of stretchable cloths 47 is mounted onboth sides of the heating body 41 as a commercially available bodywarmer. A plurality of hook-and-loop fasteners 48 is mounted on thestretchable cloths 47. The stretchable cloths 47 are laid around theboot 1, and the hook-and-loop fasteners 48 are superposed and closedtogether.

In both the cases, the open part 18 can be kept in the closed statesince the boot 1 is circumferentially constrained by the tying cords 46or stretchable cloths 47. Further, the heating surface 44 of the heatingbody 41 can be closely fitted to the outer surface of the open part 18since the heating body 41 is deformed along the irregularities of theouter surface of the bellows part 4.

Such a cloth mounting means has heat retaining effect since it is flatto cover the circumference of the boot 1, whereby the effect ofuniforming the temperature of the weld part to promote the welding canbe provided.

In the mounting of the boot 1 on the circumference of a mounting membersuch as universal joint, the universal joint is covered with the boot 1,the welding agent is applied to the opposed surfaces 18 a, 18 b of theopen part 18, and the opposed surfaces 18 a, 18 b are closed together toblock the open part 18. The closed state of the open part 18 is kept byuse of various mounting means described above. The heating body 41 isalso closely fitted to the outer surface of the open par 18 and heated.After the lapse of a prescribed time, the heating body 41 is removedfrom the boot 1. Then, the open part 18 is stimulated by the heatingeffect of the heating body 41, and heated and welded in a relativelyshort time, whereby the mounting work is completed.

According to this method, the complicated work of precisely mountingfasteners on the opposed surfaces 18 a, 18 b of the open part 18 in themanufacture of the boot 1 can be omitted, and the manufacture of theboot 1 can be thus facilitated.

For the mounting of the boot 1, the mounting of the heating body 41 onthe outer surface of the open part 18 followed by heating is sufficient.Therefore, the person in charge can leave the working site during thewelding work. The connecting work of the open part 18 of the boot 1 orthe mounting work of the boot 1 can be thus facilitated.

The welded open part 18 is excellent in sealing property because theopposed surfaces 18 a, 18 b are integrated together by welding. The workof separately applying a coating agent or sealant to the opposedsurfaces 18 a, 18 b can be omitted. The connecting work of the open part18 or the mounting work of the boot 1 can be thus facilitated also fromthis point.

Since the welded open part 18 is freely deformed according to thedeformation of the bellows part 4, the boot 1 is also excellent indeformation following property of the open part 18. Accordingly, theopen part 18 can be prevented from being broken in a short period toimprove the durability.

Performance comparative tests were performed with respect to the weldingstructure according to the embodiment of FIG. 5. The content and resultare described below.

The first performance test is the peel test of the connected open part18. The connected open part 18 was peeled with the hands, and the stateat that time was evaluated as follows.

◯: Not peeled.

Δ: 50% of the open part was peeled.

X: All the open part was peeled.

The second performance test is the evaluation of the operating state ofthe connected open part 18. After the boot 1 was integrated into a jointafter connection and rotated 10 times at a maximum angle of 40° , thestate of the open part 18 was evaluated as follows.

⊚: Not opened.

◯: One extremely small (2 mm or more) opening is present.

Δ: Several extremely small (2 mm or more) openings are present.

X: Several openings (more than 2 mm) are present.

Example 1

After the open part 18 of a split type boot 1 consisting of polyurethanethermoplastic elastomer material was welded, a heating body 41 shown inFIG. 6 was touched to the open part 18 and held for 10 minutes.

Example 2

After the open part 18 of a split type boot 1 consisting of polyurethanethermoplastic elastomer material was welded, a heating body 41 shown inFIG. 9 was touched to the open part 18 and held for 10 minutes.

Example 3

After the open part 18 of a split type boot 1 consisting of polyurethanethermoplastic elastomer material was welded, a heating body 41 shown inFIG. 10 was touched to the open part 18 and held for 10 minutes.

Example 4

After the open part 18 of a split type boot 1 consisting of polyesterthermoplastic elastomer material was welded, a heating body 41 shown inFIG. 6 was touched to the open part 18 and held for 10 minutes.

Comparative Example 1

After the open part 18 of a split type boot 1 consisting of polyurethanethermoplastic elastomer material was welded, the open part 18 was heldfor 10 minutes without applying the heating body 41 thereto.

Comparative Example 2

After the open part 18 of a split type boot 1 consisting of bolyurethanethermoplastic elastomer material was welded, the open part 18 was heldfor 30 minutes without applying the heating body 41 thereto.

Comparative Example 3

After the open part 18 of a split type boot 1 consisting of polyurethanethermoplastic elastomer material was welded, the open part 18 was heatedfor 10 minutes by use of a drier without applying the heating body 41thereto.

The test results are shown in Table 1, from which the effectiveness ofthis invention could be confirmed.

Welding Agent

A preferred embodiment of a welding agent proposed by this invention isas follows.

When the open part 18 of a split type boot 1 consisting of thermoplasticelastomer is connected not by welding with a welding agent but byadhesion or heating fusion, problems as described below might arise.

In the adhesion of the open part 18 by an adhesive, the open part 18might be peeled since the adhesive can adhere the open part 18 but notfollow the movement of the boot 1.

Contrary to this, in the welding of the open part 18 by use of thewelding agent as in this invention, the connected part can follow themovement of the boot 1 since the connecting part is integrated to theboot body.

The adhesion by use of the adhesive is not suitable for the actualassembling work (the adhering work is desirably completed within 30minutes) in a repair shop. Namely, the effectiveness is lost before thecompletion of the adhering work in case of an instantaneous adhesivetype, so that the open part 18 cannot be adhered. A general adhesive(hardenable type) requires about one night for the completion of theadhering work, and thus is not suitable for the work.

When the open part 18 is welded by use of the welding agent as in thisinvention, the assembling work can be completed within 30 minutes byregulating the kind of solvent and the mixing ratio. A preferred weldingagent proposed by this invention consists of a single body or mixture ofsolvents such as dimethylformamide, tetrahydrofuran, toluene, ethylacetate, methyl ethyl ketone, acetone, cyclohexanone, dichloromethane,N-methyl-2-pyrolidone and dibutyl ether, to which a thermoplasticelastomer is further dissolved therein to raise the viscosity of thesolution. Further, the welding agent consists of a one obtained bydissolving a thermoplastic elastomer to a mixed solution ofdimethylformamide and tetrahydrofuran to regulate the viscosity to10-10000 mPa·s, and further a mixed solution of dimethylformamide andtetrahydrofuran with a dimethylformamide/tetrahydrofuran mixing ratio of10/90-90/10, to which a thermoplastic elastomer is further dissolved toregulate the viscosity to 10-10000 mPa·s. The working time can be freelycontrolled so as to be suitable for the actual work by combining thesecomponents. The thermal fusion of the open part 18 has an unpreferableside as the actual work in a repair shop because of the necessity of afusing device (for example, solder lever, dryer, special apparatus orthe like). Contrary to this, the welding of the open part 18 by use ofthe welding agent as in this invention can dispense with such a deviceor power source.

With respect to the welding agent proposed by this invention,performance comparative tests were performed. The content and result aredescribed below.

The first performance test was the peel test of the connected open part18. The connected open part 18 was peeled with the hands, and the stateat that time was evaluated as follows.

◯: Not separated.

Δ: 50% of the open part was separated.

X: All the open part was separated.

The second performance test is the evaluation of the operating state ofthe connected open part 18. After the boot 1 was integrated into a jointafter connection and rotated 10 times at a maximum angle of 40°, thestate of the open part 18 was evaluated as follows.

⊚: Not opened.

◯: One extremely small (2 mm or less) opening is present.

Δ: Several extremely small (2 mm or less) openings are present.

X: Several openings (more than 2 mm) are present.

The third performance test is the evaluation of the easiness ofapplication work. Each welding agent was applied to the opposed surface18 a, 18 b of the open part 18, and the easiness of application quantitycontrol at that time was evaluated as follows.

◯: Extremely good

Δ: Slightly difficult to control, but there is no problem in work.

X: The viscosity is too high or too low to control.

Example 1

The open part 18 of a split type boot 1 consisting of polyurethanethermoplastic elastomer material was connected by use of a mixedsolution of dimethylformamide and tetrahydrofuran with a mixing ratio ofdimethylformamide/tetrahydrofuran=10/90 as the welding agent, and heldfor 20 minutes.

Example 2

The open part 18 of a split type boot 1 consisting of polyurethanethermoplastic elastomer material was connected by use of a mixedsolution of dimethylformamide and tetrahydrofuran with a mixing ratio ofdimethylformamide/tetrahydrofuran=50/50 as the welding agent, and heldfor 20 minutes.

Example 3

The open part 18 of a split type boot 1 consisting of polyurethanethermoplastic elastomer material was connected by use of a mixedsolution of dimethylformamide and tetrahydrofuran with a mixing ratio ofdimethylformamide/tetrahydrofuran=90/10 as the welding agent, and heldfor 20 minutes.

Example 4

The open part 18 of a split type boot 1 consisting of polyurethanethermoplastic elastomer material was connected by use of, as the weldingagent, a mixed solution of dimethylformamide and tetrahydrofuran with amixing ratio of dimethylformamide/tetrahydrofuran=50/50, to which thepolyurethane thermoplastic elastomer material was further mixed toregulate the viscosity to 500 mPa·s, and held for 20 minutes.

Example 5

The open part 18 of a split type boot 1 consisting of polyesterthermoplastic elastomer material was connected by use of, as the weldingagent, a mixed solution of dimethylformamide and tetrahydrofuran with amixing ratio of dimethylformamide/tetrahydrofuran=50/50, to which thepolyester thermoplastic elastomer material was further mixed to regulatethe viscosity to 500 mPa·s, and held for 20 minutes.

Comparative Example 1

The open part 18 of a split type boot 1 consisting of polyurethanethermoplastic elastomer material was connected by use of methanol aloneas the welding agent, and held for 20 minutes.

Comparative Example 2

The open part 18 of a split type boot 1 consisting of polyurethanethermoplastic elastomer material by use of dimethylformamide alone asthe welding agent, and held for 20 minutes.

Comparative Example 3

The open part 18 of a split type boot 1 consisting of polyurethanethermoplastic elastomer material was connected by use of tetrahydrofuranalone as the welding agent, and held for 20 minutes.

Comparative Example 4

The open part 18 of a split boot 1 consisting of polyurethanethermoplastic elastomer material was connected by use of, as the weldingagent, a mixed solution of dimethylformamide and tetrahydrofuran with amixing ratio of dimethylformamide/tetrahydrofuran=50/50, to which thepolyurethane thermoplastic elastomer material was further mixed toregulate the viscosity to 20000 mPa·s, and held for 20 minutes.

The test results are shown in Table 2. According to this, theeffectiveness of this invention could be confirmed.

In the connection of the open part 18 of the split type boot 1 accordingto the connecting method of this invention, the open curl of the openpart 18 is corrected prior to this so that the force of mutuallyseparating both the opposed surfaces 18 a, 18 b does not act on the openpart 18, and the welding is then performed, whereby the work can beeasily and effectively performed.

The correction of the open curl of the open part 18 can be performedaccording to the following method.

The boot 1 is circumferentially pressed by a fastening means such asrubber band, winding cord or winding cloth after molding, and put in athermostat (90° C. for 1 hr in case of urethane). Otherwise, the boot 1is circumferentially pressed by a fastening means such as rubber bandjust after molding, and deformed by preheat (remaining heat) (at roomtemperature for 5 hr). Otherwise, the boot 1 is circumferentiallypressed by a fastening means such as rubber band after molding, and theopposite side to the opening is locally heated and deformed.

Embodiment of FIGS. 13-16

In a split type boot 1 according to the embodiment of FIGS. 1-3,packings consisting of grommets 2, 3 of NBR are arranged on the innerside of the minor diameter-side mounting part 11 and major diameter-sidemounting part 12, respectively, to seal each mounting part 11, 12 to theshaft or outer race of a universal joint by the packing. In either oneor both of the minor diameter-side mounting part 11 and majordiameter-side mounting part 12, a required number of lip parts may beintegrally formed on the inside surfaces of the mounting parts 11, 12instead of the packings or in combination therewith so as to ensure thenecessary sealing effect by the lip parts. This example is describedbelow.

In a split type boot 1 shown FIGS. 13 and 14, the sealing property witha shaft 52 is ensured for the minor diameter-side mounting part 11 by apacking 51 consisting of a NBR grommet. A required number of annular lipparts 53 are integrally molded on the inner side of the mounting part 12as shown in FIG. 15 without providing any packing on the majordiameter-side part 12, and the lip parts 53 are closely fitted to theoutside surface of an outer race 54, whereby the necessary sealingproperty is ensured.

In FIG. 15, three lip parts 53 are axially arranged at prescribedintervals. The lip parts 53 a, 53 c on both the axial end sides aremolded so as to have rectangular sections, and the axial center lip 53 bis molded so as to have a triangular section.

Since the boot 1 is provided with the open part opened in onecircumferential part thereof, the mounting part 12 is also divided inone circumferential part. According to this, each lip part 53 and aconnecting base part 55 thereof are also divided in one circumferentialpart. With respect to this split structure, when the split end surfaces(referred also as to opposed surfaces) 12A, 12B of the mounting part 12and the split end surfaces 53A, 53B of each lip 53 and the connectingbase part 55 are arranged so as to be circumferentially displaced eachother in step-shape, the connecting area of the whole mounting part 12including each lip 53 and the base part 55 is increased. Therefore, theconnecting force can be enhanced.

When the connecting force is insufficient, the grease within the boot 1is frequently penetrated between the lip parts 53 b, 53 c. The grease ismoved along the circumference between the lip parts 53 b, 53 c. Thismight result in twisting of the boot 1. To solve this, it is effectiveto increase the connecting area more in the following manner.

Namely, a projection-like or end wall-like stepped part 56A extending inthe radial direction of the boot 1 is integrally molded on one split endsurface 12B of the mounting part 12, as shown in FIG. 16, a receiverside cutout-like or end surface-like stepped part 56B to which theprojection-like or end wall-like stepped part 56A is axially alternatelyinserted and axially closely fitted is provided on the other split endsurface 12A, and both the stepped parts 56A, 56B are mutually butted andconnected in the axial end surfaces when the split end surfaces 12A,12B, 53A, 53B are mutually connected, whereby the connecting area rateis increased, compared with the case of FIG. 17. According to this,since the connecting force is enhanced more by the further increase inconnecting area, the boot 1 can be prevented from being twisted even ifa twisting load acts on the boot 1. Each of the stepped parts 56A, 56Bhas an inside diameter dimension equal to the inside diameter dimensionof the lip part 53 (53 a). In the embodiment of FIG. 16, the material,connecting structure and other constitutions of the boot 1 are the sameas in the embodiment of FIGS. 1-3.

Embodiment of FIGS. 17, 18A, 18B, 18C

FIGS. 17, 18A, 18B and 18C show a split type boot according to a furtherembodiment of this invention.

The outline of this split type boot is illustrated. A protruding part 76formed on the split end part 74 of a boot 61 is temporarily connected toa recessed part 77 formed on the other split end part 75 in the statewhere step-shaped locking or hook portions 762 a, 772 a formed on oneside thereof are mutually engagingly locked to each other, and connectedby welding, fusion or adhesion. The protruding part 76 is hooked only inone thickness directional side. An overlapping protruding part 773formed on the non-hook side (inner side) of the recessed part 77 isconnected extending over the inside surface 76 a of the protruding part76 and the inside surface of the split end part 74 continued thereto.

In FIG. 17, the whole body of the boot 61 is molded of a thermoplasticelastomer. The thermoplastic elastomer is abbreviated as TPE. Examplesof the TPE include polyurethane thermoplastic elastomer (TPU), polyesterthermoplastic elastomer (TPEE) and the like. As the most suitableexample of such a thermoplastic elastomer, the one described withrespect to the embodiment of FIGS. 1-3 can be adapted.

The boot 61 has a minor diameter mounting part 71 formed on one axialend (transverse direction of FIG. 17), a major diameter mounting part 72formed on the other axial end, and a thin bellows part 73 formed betweenboth the mounting parts 71, 72. The bellow part 73 is formed ofrepeatedly formed mountain parts 73 a and valley parts 73 b.Circumferentially extending band mounting grooves 71 a, 72 a are formedon the outside surfaces of the mounting parts 71, 72, respectively.Bands for fastening the mounting parts 71, 72 to, for example, theoutside surfaces of the joint shaft and outer race of a universal jointare wound on the band mounting grooves 71 a, 72 a, respectively.

FIGS. 18A, 18B and 18C are sectional views taken along lines A—A, B—Band C—C in FIG. 17, respectively. FIG. 18D shows the relation of a pairof mountain part 73 a and valley part 73 b, and it is a sectional viewcorresponding to FIGS. 18A and 18B. In FIG. 18D, two split end parts 74,75 are laid in the released state where they are mutually separated.

The boot 61 has split edges or split end parts 74, 75 cut or divided inone circumferential part and mutually opposed on both circumferentialend sides thereof. The split end parts 74, 75 are opened beforeconnection as shown in FIG. 18D.

The edge or end parts 74, 75 are differed in structure depending on theaxial position of the boot 61.

In the mountain part 73 a of the bellows part 73, as shown in FIGS. 18Aand 18D, the edge or end parts 74, 75 are increased in thickness towardthe inner side. A protruding part 76 is formed on the one split end part74 of the boot 61 so as to protrude in the direction opposite to theother split end part 75. A groove-like recessed part 77 corresponding tothe protruding part 76 is formed on the other split end part 75.

The protruding part 76 is formed of, as shown in FIGS. 18A and 18D, aneck part 761 protruded from the position closer to the inner side ofthe end surface 74 a of the one split end part 74 in the boot 61, and ahead part 762 formed at the tip of the neck part 761. The head part 762has a step-shaped hook portion 762 a standing up outward from theoutside surface of the neck part 761, and an outside tapered surface 762b reduced in diameter from the periphery of the step-shaped hook portion762 a toward the tip.

An extension part 773 is formed on the inner side of the end part 75.Accordingly, the overlapping protruding part 773 extending longer than abase surface 774 a is formed on the inner side of the end part 75. Theoutside surface of the extension part or overlapping protruding part 773is formed in conformation to the inside surface 76 a of the protrudingpart 76 and the inside surface of the one split end part 14 continuedthereto. In the valley part 73 b, however, the extension part 773 is notformed as shown in FIG. 18D, and it is interrupted in an end part 773 a.Therefore, the valley part 73 b is not thickened, different from theother part, and thus relatively flexible.

In the mountain part 73 a of the bellows part 73, the outer sides of theend parts 74, 75 constitute a mutually continued surface.

The recessed part 77 has a sectional form corresponding to theabove-mentioned protruding part 76.

In the valley part 73 b of the bellows part 73, as shown in FIGS. 18Band 18D, the extension part or overlapping protruding part 773 isomitted in the part of the end part 773 a as described above. However,the inside surface 76 a of the protruding part 76 also constitutes acontinued surface together with the inside surface 75 b of the split endpart 75.

In the valley part 73 b of the bellows part 73, the circumferentialsides of the end parts 74, 75 also constitute a mutually continuedsurface.

The recessed part 77 has a sectional form corresponding to the outsidesurface of the protruding part 76. The recessed part 77 does not havethe part making contact with the inside surface 76 a of the protrudingpart 76.

In the mounting part 72 of the boot, as shown in FIG. 18C, the thickparts of the extension part or overlapping protruding part 773 and theinside surface 76 a of the protruding part 76 are omitted. Consequently,the boot mounting part 72 has substantially the same thickness over thewhole outside body. The inside surfaces and outside surfaces of thesplit end parts 74, 75 constitute mutually continued flat surfaces.

The protruding part 77 has a sectional form corresponding to theprotruding part 76.

In FIGS. 17A-17C, the upper side corresponds to the inner side of thebellows part 73.

Effect of the Invention

This invention has the following effects.

When the opposed split end parts of the boot are mutually engaged andintegrally connected by mutual hooking of the protruding part andrecessed part, a large connecting area can be easily ensured by theoverlapping protruding part. Further, the connecting strength can beenhanced, and excellent sealing property can be provided.

When the protruding part is set to the form to be hooked with therecessed part on one thickness side thereof, the split end parts can berelatively thinned. The responsiveness in repeated bending andstretching deformation can be enhanced, and the fatigue durability canbe also improved.

When the mounting parts on both the axial ends of the boot are mountedon the outside surface of a counter member such as universal jointthrough packings, the sealing property in the mounting parts can beimproved.

In the manufacture of the boot, a troublesome work of precisely mountingfasteners on the opposed surfaces of the open part can be omitted. Themanufacture of the boot can be thus facilitated.

The mounting of the boot can be performed only by mounting a heatingelement on the outer surface of the open part to heat the heatingelement. During the welding work, the person in charge can leave theworking site. The connecting work of the open part of the boot or themounting work of the boot can be facilitated.

When the material of the boot is a polyurethane thermoplastic elastomer,excellent connecting property by welding can be provided. The weldingcan be terminated in a short time.

When an amorphous bag is used, the deformability following theirregularities of the bellows can be easily imparted to the heatingbody.

When the heating body is preliminarily irregularly formed, the heatingbody can be closely fitted to not only the protruding part of thebellows but also to the recessed part thereof. The temperature can beuniformly raised. The welding time can be shortened also from thispoint.

The weld connected open part is excellent in sealing property since theopposed surfaces are integrated together by welding. The work ofseparately applying a coating agent or sealant to the opposed surfacescan be omitted. The connecting work of the open part or the mountingwork of the boot can be facilitated also from this point.

Further, since the weld-connected open part is freely deformed accordingto the deformation of the bellows part, the boot is excellent also inthe deformation following property of the open part. The open part canbe prevented from being broken in a short period, and the durability canbe improved.

TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 C. Ex. 1 C. Ex. 2 C. Ex. 3 Average Temp(° C.) of 75 80 80 73 25 25 50-90 Boot Surface in Connecting Work EndPeel Test ∘ ∘ ∘ ∘ x Δ ∘ State of Connected Part ∘ ∘ ⊚ ∘ x Δ ∘

TABLE 2 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 C. Ex. 1 C. Ex. 2 C. Ex. 3 C. Ex.4 Peel Test ∘ ∘ ∘ ∘ ∘ x ∘ ∘ Δ State of Connected Part ⊚ ⊚ ⊚ ⊚ ∘ x Δ Δ ΔEasiness of application work Δ Δ Δ ∘ ∘ x Δ Δ x Viscosity of WeldingAgent <10 <10 <10 500 500 <5 <10 <10 20000 (mPa · s)

What is claimed is:
 1. A boot comprising: first and second mountingparts formed at two axial ends, a bellows part extending between thefirst and second mounting parts, and a longitudinally extending openpart having first and second split end parts and extending between thetwo axial ends, the first and second split end parts of the open partbeing mutually opposed, the first and second split end parts of the openpart having a protruding part and a recessed part, respectively,extending between the two axial ends, the protruding part having astep-shaped hook, and the recessed part having a step-shaped hookcorresponding in shape to the step-shaped hook of the protruding part sothat the step-shaped hook of the protruding part is locked by thestep-shaped hook of the recessed part in an unjoining direction in ahook position after the protruding part is positioned in the recessedpart, whereby, after they are hooked to each other, unhooking them inthe unjoining direction is avoided, an overlapping extending partprotruding from the recessed part so that the overlapping extending partguides the protruding part when the protruding part is inserted into therecessed part, the step-shaped hook of the protruding part being withinthe recessed part when the step-shaped hook of the protruding part islocked by the step-shaped hook of the recessed part, wherein, when thestep-shaped hook of the protruding part is locked by the step-shapedhook of the recessed part, the overlapping extending part covers therecessed part and the protruding part, the protruding part and theoverlapping extending part being formed only at each inner peripheralside of the first and second split end parts so that, when thestep-shaped hook of the protruding part is locked by the step-shapedhook of the recessed part, the inner peripheral side bulges inwardly,but an outer peripheral side of each of the first and second split endparts does not bulge outwardly, the outer peripheries of the first andsecond split end parts being arranged at a same level in the hookposition, wherein all of the first and second mounting parts, the firstand second split end parts, the bellows part and the overlappingextending part are integrally made of a same material.
 2. The bootaccording to claim 1, wherein the outer surface of the first split endpart and the outer surface of the second split end part are arranged ata same level without any step or bulging portion on the outer surfacesof the first and second split end parts when the protruding part ispositioned in the recessed part.
 3. The boot according to claim 1,wherein the overlapping extending part extends over the overlaps withthe protruding part and the first split end part when the protrudingpart is positioned in the recessed part.
 4. The boot according to claim1, wherein an open part is formed by dividing one circumferential partand connected after putting the boot over a member, the open part iswelded and connected.
 5. The boot according to claim 4, wherein the openpart is welded by heating of a heating body having self-heatingproperty.
 6. The method for making a boot comprising first and secondmounting parts formed at two axial ends, a bellows part extendingbetween the first and second mounting parts, and a longitudinallyextending open part having first and second split end parts andextending between the two axial ends, the first and second split endparts of the open part being mutually opposed, the first and secondsplit end parts of the open part having a protruding part and a recessedpart, respectively, extending between the two axial ends, the protrudingpart having a step-shaped hook, and the recessed part having astep-shaped hook corresponding in shape to the step-shaped hook of theprotruding part so that the step-shaped hook of the protruding part islocked by the step-shaped hook of the recessed part in an unjoiningdirection in a hook position after the protruding part is positioned inthe recessed part, whereby, after they are hooked to each other,unhooking them in the unjoining direction is avoided, an overlappingextending part protruding from the recessed part so that the overlappingextending part guides the protruding part when the protruding part isinserted into the recessed part, the step-shaped hook of the protrudingpart being within the recessed part when the step-shaped hook of theprotruding part is locked by the step-shaped hook of the recessed part,wherein, when the step-shaped hook of the protruding part is locked bythe step-shaped hook of the recessed part, the overlapping extendingpart covers the recessed part and the protruding part, the protrudingpart and the overlapping extending part being formed only at each innerperipheral side of the first and second split end parts so that, whenthe step-shaped hook of the protruding part is locked by the step-shapedhook of the recessed part, the inner peripheral side bulges inwardly,but an outer peripheral side of each of the first and second split endparts does not bulge outwardly, the outer peripheries of the first andsecond split end parts being arranged at a same level in the hookposition, wherein all of the first and second mounting parts, the firstand second split end parts, the bellows part and the overlappingextending part are integrally made of a same material, said methodcomprising the steps of putting the boot over a member, thereaftersetting a heating element having self-heating property to an open partof the boot, and welding the open part.
 7. The method according to claim6, wherein a welding agent provided on the open part is heated by theheating element so that the open part is welded.
 8. The method accordingto claim 7, wherein the welding agent is applied to one or two surfacesof the open part so as to weld and join the surfaces together.
 9. Themethod according to claim 8, wherein the welding agent includes at leastone of dimethylformamide, tetrahydrofuran, toluene, ethyl acetate,methyl ethyl ketone, acetone, cyclohexanone, dichloromethane,N-methyl-2-pyrolidone, and dibutyl ether.
 10. The method according toclaim 7, wherein the welding agent consists of a solvent for dissolvinga thermoplastic elastomer.
 11. The method according to claim 6, whereinthe open part is formed by dividing one circumferential part of theboot, and thereafter a welding agent is applied to the open part and isheated by the heating device so that the open part is welded.
 12. Themethod according to claim 11, wherein the heating device is deformable,and the heating device includes an amorphous bag containing a heatingcomponent.
 13. The method according to claim 11, wherein the heatingdevice has a bellows-form corresponding to a bellows-form of the boot sothat the heating device is closely fitted to the open part along thebellows-form of the boot.